Lesson 07 · Claude Mastery Pro ~9 min read 4 sections + anti-patterns

Custom instructions: teach Claude once.

Most Claude users either skip custom instructions entirely (and get generic output forever) or write them so badly they make Claude worse. There are four sections every good instruction set needs, plus three anti-patterns that make Claude noticeably worse. This lesson covers both.

The mental model

Custom instructions are a contract Claude signs at the start of every conversation.

They tell Claude who you are, how you work, and what you want. Done well, they replace pages of re-explanation. Done badly, they confuse Claude into worse output. The skill is writing them tight.

Workflow 01 The 4 sections every instruction set needs

1

Structure your custom instructions

Custom instructions in Claude should cover these four areas, each in 2-3 sentences.

The prompt that works

TemplateABOUT ME: I'm [role] at [company/industry]. I primarily use Claude for [main use cases]. MY VOICE: [Conversational/formal/direct.] Avoid [jargon, AI clichés, specific phrases you hate]. Use contractions / Don't use contractions. MY PROCESS: [How I prefer to work with you. Ask questions before assuming. Show your reasoning. Don't over-explain.] DEFAULT BEHAVIORS: [Be concise unless I ask for depth. Flag confidence when uncertain. Never invent statistics.]

Best use cases

  • Anyone using Claude weekly+
  • Founders, writers, professionals with distinct voice
  • Engineers with strong opinions about code style
  • Anyone tired of explaining the same context
Don't put confidential info in custom instructions — they're stored. Keep it about style and process, not specific facts or sensitive details.
Time savings: Re-explaining yourself: never again.

Workflow 02 The three anti-patterns that make Claude worse

2

Avoid these common mistakes

Some instructions actively degrade output quality. Watch for these.

The prompt that works

Anti-patterns1. Conflicting rules: "Be detailed but concise" — pick one. 2. Over-constraint: 20+ rules → Claude becomes paralyzed. Aim for 6-10 strong rules max. 3. Style without substance: "Be helpful and clear" — too vague to change anything. Be specific: "When I ask for code, show the full file, not snippets."

Best use cases

  • First-time Claude users writing too many rules
  • Anyone whose Claude output got worse after they added instructions
  • Teams sharing a Claude account with conflicting style preferences
Test your instructions: ask Claude something, then check if the output reflects your rules. If not, the instructions aren't doing what you think.
Time savings: Output quality immediately improves when instructions are tight.

Workflow 03 Iterate on your instructions like code

3

Update them every 4-6 weeks

Custom instructions should evolve as your needs change. Treat them like a config file you maintain.

The prompt that works

Iteration patternEvery month or so, ask: 'What kinds of output am I still editing heavily?' Update instructions to bake that editing in. Add rules for the friction; remove rules that stopped mattering.

Best use cases

  • Anyone serious about Claude as a daily tool
  • Long-term users whose use cases have evolved
  • Teams converging on shared best practices
Don't bloat. If you can't fit your instructions in 10 sentences, you're trying to do too much.
Time savings: Tool fit gets sharper every iteration.

Final challenge: rewrite your instructions tonight

Open Claude settings. Either: (a) write your first real custom instructions using the 4-section template, or (b) if you already have them, audit them against the anti-patterns. Trim to 10 sentences max. Test with 5 typical prompts. Notice the difference.

Back to Claude Mastery → See pricing →

What you can do now

  • Write custom instructions using the 4-section structure (About, Voice, Process, Defaults)
  • Avoid the three anti-patterns (conflicts, over-constraint, vague style)
  • Test your instructions by running typical prompts and checking the output reflects them
  • Treat custom instructions as code: maintain, iterate, prune
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Up next in Claude Mastery

Lesson 8+ · Plus: agents, MCP, advanced patterns, and more

Multi-turn agent workflows, connecting Claude to external tools via MCP, prompt chaining, evaluation patterns. The advanced curriculum for power users. See pricing →